Variable area nozzle for hightemperature turbines



Sel/at. 8, 1953 B. o. BUCKLAND ET AL VARIABLE AREA NOZZLE FORHIGHQTEMPERATURE TURBINES Filedoct. 1o, 1951 2 Sheets-She??l 1Inventors: Bnuce OBLACKIanOl, Glenn BWarT'fen,

by A

Their` Attorneys.

Sept- 8, 1953 BL o. BUCKLAND ET AL 2,651,496

. VARIABLE AREA NozzLE FOR HIGH-TEMPERATURE TURBINES Filed oct. 1o, 1951A 2 sheetssheet 2 aga.

Inverwtcprs: use BUCK lanci lerwn Ewen-'hem by mw Their Attorney.

Patented Sept. 8, 1953 UNITED STATES PATENT OFFICE VVARIABLE AREA NOZZLE FOR HIGH- TEMPERATURE TURBINESl Bruce 0. Buckland, Schenectady,and Glenn B. Warren, Niskayuna, N. Y., assignors to General ElectricCompanna corporation of New York Applicationfoctober 10, 1951, SerialNo. 250,738

(Cl. 253-78)l Claims. l

'This invention relates to adjustablenozzles for high temperatureturbines, as in gas turbine power plants where it is necessary to effectoptimum turbine efficiency over a wide range of conditions.

It has for some time been appreciated by gas turbine designers that, ina turbine intended for operation over a wide range, it is highlydesirable that the effective area of the turbine nozzles be adjustable,in order to obtain better performance at light load conditions, bettercontrol in the event of overspeed, improved operation at varying ambienttemperatures, to permit a reduction in the power required to start theplant, and for various other reasons. In steam turbine design, this hasbeen accomplished by subdividing the nozzle ring into a plurality ofarcuate segments and separately controlling the iiow of motive fluid tothe respective segments by valves, which are successively opened as theload output is increased. Although not the most efficient way to effectnozzle area variation, this expedient has been widely adopted because ofits mechanical simplicity, as compared with the extreme diicultiesencountered in building a nozzle structure which will continuously varythe area of the whole nozzle ring. Y

In gas turbine design, where the overall elllciency of the power plantis intimately related to the thermal eiciency of the turbine per se, itis of the utmost importance that all available means be used to obtainevery slightest improvement possible in turbine eiilciency. In suchpower plants, turbine efficiency is therefore sufciently important as towarrant the increased mechanical complexity required to make lthe entirenozzle ring of continuously variable area, between certain limits.

Accordingly, the object of the present invention is to provide a hightemperature gas turbine nozzle ring arrangement in which the separatenozzle blades may be rotated through a limited arc to vary continuouslythe elective area of the entire nozzle ring.

Another object is to provide a variable turbine nozzle of the typedescribed, arranged to p ermit the substantial differential thermalexpansion which must take place between the nozzle blades and theassociated annular walls between which the nozzle blades are supported,without imposing excessive stresses on either blades or sup in which-clearances are provided between the re` spective moving parts of thenozzle proper, with special arrangements for keeping these clearancesfree of dirt to prevent binding of the movable parts, while at the sametime maintaining these clearances at aV preselected minimum value whichremains substantially constant for all positions of the adjustableblades.

Other objects and advantages will become apparent from the followingdescription taken in connection with the accompanying drawings, in whichFig. 1 is a partial longitudinal section of a multi-stage axial iiow gasturbine having a nozzle ring incorporating the invention interposedbetween two stages, Fig. 2 is an enlarged detail view showing theresilient supporting arrangement for the inner wall of the motive fluidpath, Figs. 3-6 inclusive are detail views of the spring biasing meansincorporated in the resilient inner wall support, Fig. 7 is a detail endview of the inner segmental nozzle wall, taken on the plane 'l-l in Fig.2, and Fig. 8 is a cross section view of one nozzle blade.

Generally, the invention is practiced by supporting the adjustablenozzle blades between inner and outer segmental walls which havespherical surfaces cooperating Iwith the ends of the blades. Specialspring and air pressure biasing means are provided for maintainingconstant the clearances betweenthe blades and wall segments.

Referring now more particularly to Fig. 1, the invention is shown asapplied to a turbine having two mechanically independent rotors, I and2, supported in a common casing 3. The respective bucket-wheels areprovided with circumferential rows of radially extending blades la, 2a,and are supported in separate bearings (not shown). The detailedstructure of the bucket-wheels and the method of fastening thel bladesto the disks are not material to an understanding of the presentinvention and, therefore, will not be discussed further herein.

The casing arrangement includes an outer casing member indicatedgenerally at 3a. and an inner casing assembly 3b. To facilitatemanufacture and assembly, the outer casing member 3a is formed in two ormore arcuate segments bolted together, while the iirst inner casingmember 3b is a solid continuous ring. This inner casing 3b is supportedfrom the louter casing 3a by a plurality of radially extending hollowstuds 4. Specifically, there are six of the tubular studs 4. and thepassages therethrough serve as conduits for air underpressure, asdescribed more particularly hereinafter. It `will bey apparent` fromFig.' 1 that each stud 4 has a radially extending flange 4a welded to orformed integral with the outer end thereof. The anged end 5a of suitableair inlet conduits 5 abut the outer faces of the flanges 4a. The flangeportions 4a, 5a are secured to the split casing 3a by a plurality ofthreaded fastenings 6.

The inner and outer walls of the motive iiuid flow path upstream fromthe nozzle ring are formed by segmental wall portions Ea., 1a. The outerwall segments, of which there may be twelve, for instance, are providedwith axially spaced tongues or dovetails 8,' Sl. These 'dove= tailsposition the segments 6a in a radial'and in the axial direction.Assembly of the segments into their annular groove'in casing 3a ispermitted by the fact that this casing is split along one or more axialplanes, asnoted above.

In order to reduce the transfer of heat from the hot outer wall segment6a to the casing member 3a, the segments engage the casin-g only in theneighborhood of the dovetail supporting portions 8, 9, there beingcircumferential spaces between segment and casing as indicated at I0,Il, I2. These dovetails 8, 9 extend circumferentially only a smallportion of the complete circumference, which further reduces the heatflow to the casing, also reducing the bending stress in the segments. Inorder to prevent the circulation of hot motive iiuid into thesecircumferential spaces and past the segments, the spaces are occupied bythin sheet metal rings of Z-shaped cross-section, as shown at I3, I4,I5. These rings also denne additional dead-air spaces between theirouter surfaces and the adjacent wall of casing 3a so as to function asradiation shields, further reducing the transfer of heat by radiationand convection from the hot segments 6a to the casing 3a.

The inner wall segments 1a are likewise supported by a tongue ordovetail portion IB. Since the first inner casing 3b is an integralstructure, not split as is the outer casing 3a, assembly of the segment1a is permitted by the fact that the inner casing 3b is detachablyconnected by screws I1 to a second separately fabricated inner casingmember 3c, which is also an integral annular ring.

In order to reduce the transfer ofheat from the motive uid to thesupporting stud landair conduit members 4, a streamlined shroud I8 isdisposedaroundeach stud 4. The shrouds I8 may be loosely disposedbetween the inner Aand outer segments 1a, 6a, or they ymay be welded toone of the segments.A As disclosed in Fignl, the shroud I8 is welded tothe inner segment 1a and has an end plate member I9 welded in the outerend of the shroud and having a Central opening through whichthe stud- 4passes with a very Ysmall clearance therebetween. A There is suicientclearance between the end of the shroud I8 and the adjacent wall ofsegment 6a that differential thermal expansion of the shrouds will notcompletely close up this clearance Iand impose axial compressive forceson Vthe comparatively thin shrouds.v Because of this clearance betweenshroud I8 and segment; 6c, and that between segment Ga and stud 4, thesheet metal annularV shield I4 is particularly necessary to preventheattransmission to the shells by hot motive duid leaking outward and inwardalong the surface of the stud 4.

In order to supply cooling air toAthe downstream face of the firstbucket-wheel I and the upstream face of the second bucket-wheel 2, theinner casing ring 3b is provided with .a sheet 4 metal casing indicatedgenerally at 20. This casing has a central chamber 2l defined betweenaxially spaced plates 2 Ia, 2 Ib. Plate 2 Ia is welded to plate 28 asshown at 22 and the outer circumference of plate 2lb may be tack-weldedto the inner circumference of casing 3b, as shown at 23. Casing alsodenes an vouter annular chamber 24 vformed by an annular member 25 whichmay be tack-welded to casing member 3b as shown at 26. Cooling air issupplied to the central chamber 2I through one or more of the hollowstuds 4, to passages indicated in dotted lines at 21, Fig. 1, 'a'iid by'Way of .a connecting tube 28. It will,

and tubes 4 and 28 with which it communicates are actually behind theplane of Fig. 1, since other passages (to be described hereinafter) areshown in full lines as being in the plane of Fig. 1.

- Cooling air supplied at a suitable pressure through the studs 4 to thecentral chamber 2I is admitted to the spacesad-jacent the respectivebucket-wheels I, 2 by restricted central openings 2 Ic, 2Id. The shroudwall portion 25 causes the cooling air from port 2Ic to flow in closecontact with the downstream face of wheel I, and the iiow of hot motiveiiuid backward into this space is limited by circumferential packingrings 28, 30 secured to radially spaced portions of the casing member 3band forming close clearances with circumferential surfaces on the wheelI.. Cooling air from the annular space adjacent wheel I eventually leaksoutward into the motive fluid 4liow path as indicated by arrow 3| inAFig. l. Likewise, cooling air from the port 2Id flows over the upstreamfaceuof the second stage Wheel 2, past sealing rings 32, 33 and entersthe motive fluid ow path as indicated by arrow 34. Thus it will be seenthat the turbine Wheels are cooled by separate air streams from chamber2|. The flow is equalized circumferentially around the wheels by thegenerously proportioned concentric annular spaces defined between thewalls 2Ia,v25, 3b, 1a and wheel I, and walls 2lb, 3c, 1 la and wheel 2,respectively.

This invention particularly relates to the adjustable nozzle blades forthe4 second stage buckets 2d, sho'wn at A'35 in Fig,l l. Each adjustableblade 35 is secured. to a rod 36 supported for limited rotationalmovement ina bushing assembly 31. The adjustable vanes or blades 35 maybe forged, machined `'from bars, or fabricated from sheet metal. Asshown in Fig. 1, they are solid forged or cast blades, having anair-foil cross section of the shape shown in Fig. 8. In order to reduceheat transfer from the blades 35 to the rods 38, the red forms asubstantial clearance space throughout a lar-ge portion of its lengthwhich projects into the blade, as indicated at 38 in Fig. l. The extremeinner end portion of the rod 38is welded as shown at 39 to a circumferential lip formed in arecess in the end of the blade. Thus, the blade 35is permitted to ex-A pand longitudinally relative to the rod 35, whilethe rod is kept comparatively cool by reason of conduction of heat alongthe rod, taken in combination with the restricted rate of heat transferfrom blade to rod.

The bushing assembly 31 is cooled by water, which may be admittedthrough a supply conduit 48. Ihis coolant venters an arcuate groove 4Iformed in the outer surface of bushing 31 whence it flows by one or moreradial holes 42 into onev or more longitudinally extending grooves 43.At the inner ends thereof, the grooves 43 communicate with an annulargroove 44,v which in Vturn communicates with axially extending grooves45.Y Radial. holes 46 conduct the used coolanttaan arcuate groove 41vwhence it leaves by drain conduit 48.'A The supply conduits 40 anddrain conduits 48 forthe respective bushings 41 are, of course,connected by circumferential manifolds which may be either externalpipesv (not shown) or, alternatively, may be formed as .circumferentialpassages in the casing 3a A,(not shown). Flow of' i coolant inwardbetween bushing 31and casing 3a is preventedby a packing'ring seal 49,and leakage of coolant between rod36 and bushing 31 is,prevented byadditional packing rings 5l), 5l.- The outerV end of bushing 31 isprovided with a radial flange 31a, secured by threaded fastenings 52 tothe outer end of a boss formedintegraly with casing 3a. f

TheA means for Vadjustably positioning the rods..36 includes an` axiallyprojecting lever member 53 having one end pinned vto the outer end ofrod 36 as indicated at 54. A coil spring 55 is interposed between theouter face of flange 31a and the adjacent face of rod end-,portion 53a.This spring helps to take up looseness between the respective nozzleparts during assembly and when the. plant is shut down. The otherend ofeach control lever 53 is pivoted at 56 to a link 51 which is in turnpivoted at 58 to a control ring 59, which `ring extends entirely aroundthe outer circumference of the power plant. The arrangement of levers53, links 51 and the control ring 59 may be seen more clearly in theelevation view shown in the lower portion of Fig. 1. The control ring 59is rotatably supported by a plurality of circumferentially spacedrollers 60, 6| as shown in the upper sectional portion of Fig. 1. Theserollers engage inclined annular surfaces 59a formed on the innercircumference of ring 59 asr will be apparent in Fig. 1. Rollers 60, 6Imay be conveniently supported on threaded stud members 62 projectingoutward through holes in a ring 63 of V-shaped cross section. Therollers may, of course, be retained on studs 62 by suitable retainingnuts 62a or the equivalent. The V- ring 63 may be secured, as bytack-welding, to inner member 64 which seats on aplurality ofprojections 65 integral with the casing 3a. To permit assembly of thecontrol ring 59a in position between rollers 60, 6|, vthe ring must beformed in two or more arcuate segments, which may be bolted together byprojecting flanges 66, 61.

It will now be apparent that circumferential shifting of the controlring 59 will cause the levers 53 to simultaneously rotate the rods 36.This circumferential shifting of the control ring may be effected by anysuitable electrical or hydraulic motor means (not shown). In an actualpower plant, this shifting will be accomplished by a motor under thecontrol of a suitable regulating system.` The specific regulatordeveloped for adjusting this particular nozzle structure is disclosedmore completely in the copending application of Neal E. Starkey, s N.252,916, filed October 24, 1951, now Patent No. 2,625,789, and assignedto the same assignee as the present application.

Perhaps the most important single problem encountered in variablenozzles of this type is that of preventing excessive leakage between theends of the adjustable vanes 35 and the inner and outer Walls with whichthey cooperate, without at the same timel risking seizure be- 6, tweenthe vanes and their cooperating walls due to expansion and forceddeflections of` the parts, and due to deposits of dirt accumulatingduring operation. In the present arrangement, this is effected in thefollowing manner.

. The outer wall member with which the vanes cooperate is not acontinuous annular ring but a plurality of segmental members, vone ofwhich is Yshown in section at 68, Fig. 1. YThe inner sur-.- face 68aisnot a cylindrical surface about the axis of the power plant, but isspherical, with a center located on the axis of the rotor. Thecooperating end of blade 35 has a spherical portion adapted to engagethe spherical surface 66a,

Vbut the rearward or trailing edge portion of blade 35 is relievedsomewhat to provide a clearance shown at 68h. This is to reduce thefriction area between segment and blade and thus reduce theturningeffortrequired from the positioning motor means, and to permit completely freedifferential thermal expansion between the comparatively thinnertrailing edge of the blade relative to the segment 68. This avoids thepossibility of imposing excessive compressive forces onthe thin trailingedges of the blades when motive fluid is first admitted to the turbine,as might otherwise occur since the trailing edges will naturally heat upfaster thanthe comparatively heavier section through -which the rod 36passes. This also allows shearing of any dirt deposits which may form onthe end walls, with minimum torque on the blades.

In order to prevent axial shifting of the segments 68, as well as toprevent leakage of motive fluid around the outer surface thereof, eachsegment is provided with a radially projecting circumferentiallyextending tongue 68o, which is received in an annular groove in casing3a.

Interposed between the outer surface of segments 68 vand the casing 3ais a thin segmental sheet metal band 69. An annular washer 10 isinterposed between the outer surface of segmental band 69 and the end ofbushing 31.k To reduce heat transfer from the outer segment v68 to thebushing assembly, the outer surface of the segments may be recessedslightly to define clearance 68d, 68e, so that the segment 68 engagestheband 69 only on an annular area immediately surrounding the rod 36. Theinner boundary of the motive vfluid flow path is formed byacorresponding series of seg- -l ments, one. of which is shown insectionzat 1l, Fig. 1. The number of segments 1I is, of course, equal tothe number of segments 68 and in the present structure there aretwenty-four adjustable blades 35, and twelve circumferentialsubdivisions of the segments 68, 1I. In other words, there are twoadjustable blades 35 for each cooperating pair of segments 68, 1I. Theouter surface of segment 1| is provided with a spherical surface 11a.This spherical surface also'has its center at the, axis of the powerplant. Here, again, the trailing edge of the blade 35 is recessed todefine a clearance space 1lb, analogous to the clearance 68h describedabove. j f Y "The' segments -1lv are supported on vthe second innercasing member 3c by circumferentially extending flanges or dovetails 12,13. It Will be seen inFig. l that these dovetails have axiallyprojecting inner end portions projecting loosely into annular groovesdened in the side faces of circumferentially extending flanges 14, 15,respectively. Assembly of these segments 1| to the integral casing 3c ispermitted by the fact. that 7 the segments are `inserted radially intoposition relative Lto the danges 154, 15 before fthe 3c iis ibolted tofthe first innerf casing fab. rThe faxiel vdimensions :of lthe :groovesin fthe .outer `surface of casing 3c are .such that the :segments 5H manhe Aassembled radially :and Athen slid axially to the right so `that the:dovetails 12, 33 :engage fthe ilanges 14, f1.5, Las show-n il. casing3c is :subsequently secured Eby `.bolts 'SISI to fcasing 3b, theYcircumferent'ial ange portion 16 mi eas- .ing 3c :serves :as a.retaining :wall fior :dovetails fit .of the segments 1a. ltlle :sametime 'the Aada'cent edge :portion of :segments 1a. .serve to preventsegments "III trom fsh'itting to the left far enough to -disengagee'from easing 3c.

.Sealing Aagainst leakage between Athe ends fof adjacent segments 1| :isprovided :by fthe interlocking tongue and groove arrangementshown inFig. 7. 'This .View is itaken :in 4the direction of arrows 1 -7l, Eig.2., :and 'fit .will he seen that, with two exceptions, each .segment'5.1i has .a radially -inner proeotingiportionshownat 11j ,on seg.- ment.'lllc, YWhile at `the .other .end the segment is provided with :a4radially .outer axially :extending 4edge portionfll'g. ln order topermit assembly, one segment '5l-ld, is .provided at -both ends ywith :aradially .inner Aedge portion "lfllj, while '-the next .adjacent:segment ille is provided .at .both ends with radially :outer edgeportions .1:th. 'With .this arrangement, :segment TH d is insertedilrst, .then the .segment 15| c, 1and vso y.on around the ring-icoufnterclockixzise, .untilsegment 1ste is inserted last.

Means are v.provider-.l for ,preventing excessive looseness of the.segments '.1:|, :adjustable -hlades 35, segments $8', .and irelated'.parts, as ffo'llows. It -wlill be apparent in Fig. 2 that .the:outersurface :of casing portion 53o between the flanges T4, lvforrns:anzannularrecess .11 with the iinnerA surfaces .of fsegements 2TH.v`nir under vpressure is supplied to this annular .fohamb'er f by one`or more passages, :shown :in iEig. 1 ias "being `formed by drilledholes .'lfB, 119. yAir .under '.pressure, ias for :instance from fassuitable point in the .compressor associated with vthe gas turbine:power plant (notshown) :isrsupplied '.by wayf pne yfor more .of #the:hollow studs f4 to the :passages 59, -18 .and 'the chamber 15|. Thus,:there eis 1.huilt :up in chamber 1?! :a vfluid v:pressure tending'.bilas the segments 'lll radially outward so athat .feach segment FM isheld in :engagement with l:the inn-er ends :of the zrelated :blades '35.Also fthe fouter ends .of iblades 35 :are dirmly pressed against .theadjacent :surface .of segments 68, :and the .segments F68 are 'in fturnlbiased .against fthe band #69 and washers flihus, the :substantial.degree of looseness required -Lbetween these parts fin rorder to permitfree differential thermal expansion is prevented `rfrom introduoingiundesirable vibration .of *these :parts :in :normal operation.

In aorder to prevent :accidental .displacement .of these comparatively:loose parts when the Yplant is :shut downand :during the .startingprocess, :additional :biasing means may be f-associated withithexinnersegments H. This sspringlbiasing arrangement is seen more clearly inFig. 2, fand is omitted ffrom Fig. lbecause of the small Vscale of vfthedrawing.

The-.inst spring is :indicated *at 80, .beingrepre sented in end "Viewiin Fig. This spring is actually fan elongated 'leaf spring having azplan form zas shown in Fig. .3 'and lbent to :the ishape shown in Fig.4 .-As will 4be seen 'most vclearly in Alliig. 4, 'the lcentral :portionvof ithe leaf spring is lprovded with an arcuate @depression extend-'ing transversely :across ithe spring. recess Z.is .provided for the'passage :of a fdowel pin .shown partly "in ldotted :lines .at 8l Fig.2. 'This .dowel is inserted through a drilled hole 82 in the lcasingflange @portion 11B and projects through an arcuate recess formed 'inTthe :segment da-nge portion T112, through a drilled ,hole :inzthe.casing flange 4portion TM, ,projects through vfthe chamber lll, throughan arcuate :recess in the :segment flange .portion T3, .and 'terminatesin a dmrled hole in casing @flange .portion 35.. .Once'thecasing portion3c 'is bolted ."to casing 3b', fthe dowel pns 81 are, of course,prevented imm leaving ithe positionfshownin F.ig.12. .It will abe.apparent that they lserve :to maintain the-segments FH in longitudinal:alignment :relative to the .casing ic, against 'the :action .of thekfriction 4forces acting on the segments when the vanes 35 arecaused .tolAt the saine time, the segment il is loosely .supported for :limitedrocking :movement about the .pin 181 .so .that the .rend of 'the'lola-de 35fcan adapt itself to thesurfacerof lthefresiliently supportedsegment 12|. Since .the leaf .spring 8U is disposed between the dowelspin 81 .and :the outer vsurface of casing .portions .-3c, vthe springloosely retained in the position :shown iin Fig 2. 'It willbe :obviousthat the-ends yof the leaf spring '80 are biased upwardly .against :the:under surface 'ci segment 'TH so las to hold .it `.linengagement withthe :inner `end fsuraces =of venes 35. Thus, the radial clearancesbetween the erespective parts are held closed :when 'the power plant isshut down so 'there Y.Will '.be .no 'undue looseness during the startingcycle.

'The resilient support fior the segments FH 1includes a second .set :oflleaf springs, .1an end :View of .one of which shown at 83, Fig. 2.Theplan formof vthisspring is shown .iniFig 5, .and fit `is bent "to theshape shown iin Fig. r6. 'For retaining this #spring against.circumferential displacement in the .recess dormedbetweenlflange f1.6and flange 12, :each 'lea spring 83 #may Ihre provided with an .axiallyprojecting .end `tang u83a, which is Areceived lin'a recess formed'inthe-adjacent fface of Vange 31.2, as :shown inFig 2. Itwillbeepparent from a `consideration vof Fig. f2 Athat fthe functionofythese springs 2'8'3 fis to bias .the segment l'sl axially to theVrigh-t.

Fig. 2 actually represents fthe icoldfcondition, in which springsf'lhiasithe-ange 32 iintoengagement `with the circumferentiallyLextending ipaoking teeth Ha machined on casing flange 11. Whenoperationhegins :and the segment TH ibegins to expand in an axial direction, thedifferential therma'l .'.expansion relative 'Lto vthe comparaltivelycooler casing eporti'on '3c .causes the .clearance spaoe. shown "at 13akto fclose :up Thereafter, urither thermal expansion of segment TM iinYan axial :direction vWill result in a "clearance space opening11p-between 'theteethlila and the flange 12. lWhen the mach-ine cools,segment 1l `again grows shorter lin the lairial :direction ewith the =result that springs L83 loi-as it to lthe 'position show-n in iFig.

It .may :be noted :that the segments 36a; 68, 5l-a, and lilwillordinarily .be-.made-.of atemperatureresisting alloy, :such .asea-n.austenitic fsteel, 1wl1'ile easingcdsaof vaalovver :temperature alloy,:anchoas a ferritic steel. Since the .austertic sal-ley hasta much4higher .eoefdient'of :thermalexp ansion, the above-describeddifferential expansion :effect is enhancedand will :occur .even when.the parts are at -Lthesame temperature zinnormal operation.

iIt'will -be -apparent 'that ithesdual :pressure vand leaf springbiasingarra'ngement insures that :all

, 9 parts of the variable nozzle arrangement will be held firmly indesired position when the machine vis cool, yet permits them to freelyexpand in accordance with differential temperature changes when themachine comes up to normal operating temperature.

In addition to the biasing function described above, the pressurizingair admitted to chamber 'l1 performs the very important additionalvfunction of keeping clean the clearance spaces between the respectiveparts. ItWill be obvious that there will be some leakage from thechamber 11 past the packing teeth 14d and through the clearance spacebetween flange 'l2 and segment 1a, as well as through the clearanceidentified 13a in Figure 2. This small outward flow of leakage fluidwill prevent the entrance of carbonized fuel particles or other dirtentrained in the motive fluid. Without this cleaning function performedby the pressurizing fluid, foreign particles might build up in theseclearance spaces to such an extent that free differential thermalexpansion between the parts would be prevented.

vWith this arrangement, the nozzle parts are kept free to adjustthemselves with respect to the movable blades 35, and to expand andcontract in accordance with temperature changes.

Thus, it will be apparent that Vthe invention provides a novel variableturbine nozzle construction in which complete freedom is permitted forthe relatively movable parts to expand and contract in accordance withtemperature changes and to provide a certain degree of self-aligningaction between the segmental inner andouter wall portions and thecooperating end portions of theV adjustable nozzle blades, whileemploying special spring and pressure biasing arrangements for holdingthe loosely fitted self-aligning parts firm against vibration.

While the invention has been described as applied to a high temperatureturbine, those skilled in the art will appreciate that it may also haveapplication to lower temperature turbines or to variable guide vanes inaxial flow compressors. It will be obvious to those skilled in the artthat many changes and substitutions of mechanical equivalents may bemade. For instance, for operation in some temperature ranges theclearances between the movable parts may be made sufficiently small thatthe special spring biasing arrangement, including the leaf springs, 80,83, may be dispensed with and the pressure biasing arrangement usedalone. Likewise, many other arrangements for adjustably positioning thecontrol rods 36 might be employed.

It is, of course, intended to cover by the appended claims all suchmodifications as fall within the true spirit and scope of the invention,

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. In a variable guide-blade arrangement for an axial flowturbo-machine, the combination of an annular outer casing, an annularinner casing assembly spaced radially from the outer casing to define amotive iiuid flow path, a plurality of circumferentially spacedrotatably adjustable control rods supported in the outer casing withtheir axes substantially radial and their inner ends projecting into thefluid iiow path and each carrying an airfoil-shaped blade for directingthe fiow of fluid, the inner casing assembly comprising first and secondannular inner casing members, the radially inner wall of the fluid flowpath being defined by a first circumferential row of arcuate segmentsloosely supported from the first inner ylll casing member, the segmentsupport means comprising a radially projecting flange portion extendinginwardly from each segment and having an axially extending portionengaging an -annular dovetail groove in an adjacent end surface of thefirst inner casing member, the second annular inner casing member beingremovably secured to said first inner casing member and having aradially extending flange portion overlying the .adjacent radial surfaceof said segment support dovetail flanges whereby, whenthe first andsecond inner casing members are secured together,

said segment support dovetail flanges are prevented from disengagingfrom said dovetail grooves, the second inner casing member supporting asecond circumferential row of wall segments forming a second portion ofthe inner fluid flow path, each of said second-mentioned segments havingat least one portion of spherical shape, the inner end of each bladebeing shaped to define constant clearance spaces with the abuttingsegment in all positions of the blade, each of said second row of wallsegments being secured to the second innercasing member by a pair Vofaxially spaced circumferentially extending dovetail flanges l eachincluding a' radially inwardly extending wall portion and an inner endportion extending axially awayv from said first inner casing member andengaging circumferential grooves in a pair of cooperating axially spacedcircumferentially extending flanges projecting radially outward fromsaid second inner casing member, said first row of inner Wall segmentshaving circumferentially extending edge portions projecting axiallytowards the second row of inner wall segments -and defining therewith acircumferential clearance space of such width that said second innerwall segments are prevented from moving toward the first row of segmentssufficiently to disengage the dovetails supporting the second row ofsegments, said second inner casing member defining a pressure chamberbetween said axially spaced circumferentially extending dovetailflanges, and conduit means for supplying fluid under pressure to saidpressure chamber whereby said spherical surfaces of the second row ofsegments are biased radially outward into engagement with the adjacentends of the adjustable blades.

2. Variable guide-blade structure in accordance with claim 1 andincluding leaf spring means engaging the second inner casing member andbiasing the second row of segments axially toward the segment supportdovetail flanges of the second inner casing member.

3. Variable guide-blade structure in accordance with claim l andincluding leaf spring means disposed in the annular pressure chamber andhaving portions engaging the second inner casing member and the secondrow of inner wall segments for biasing said segments outwardly intocontact with the blade end portions when the machine is inoperative andthere is no biasing pressure fluid supplied to said chamber.

4. Variable guide-blade structure in accordance with claim l andincluding an axially extending doWel pin, there being one pin for eachof the second row 4of wall segments, each pin being disposed through anaxial hole in the first and second axially spaced radial flangesextending outwardly from the second inner casing member and terminatingin a hole drilled part way through the third radial flange of the secondinner casing member -most remote from the first inneroasing aesinet;

member, the 4cooperating segment .being provided with cut-out portionsin the xdozvetail flanges thereof, said cut-out portions 'being adaptedto receive the dowel pin for maintaining axial ,alignment of the segmentrelative tothe inner casing member, the clearances between saidsegment., the support anges of the second inner casing member, and theadjacent edges Vof the Ilrst row of inner wall segments being sufficientto permit limited self-aligning adjustment Vof the second row ofsegments relative to the dowel pins.

5. in ,a 'variable guide-blade arrangement for an axial nowturbo-machine, the'cornbination of an annular outer casing, an annularVinner casing assembly spaced radially *from the outer casing to definea motive `fluid 'new path therebetween, a plurality of circumferentiallyspaced rotatably adjustable control reds supported the outer casing withtheir faxes Vsubslaaz-niially Irenlial and their Vinner ends projectinginte fluid new path and each carrying an air-oli-shaped blade fordirecting the ilow of uid, said inner casing assembly comprising irstVand .second annular inner casing members with means detachably securingthe two together, means supporting the rst inner casing member from theouter casing, the radially inner Wall of the fluid flow path being denedin :part by a circumferential row of arcuate wall segments each haringat least .-one portion of spherical shape, the inner end of each bladebeing vshaped. tao-define constant clearance space with a sphericalportion of .an abutv,ting segment in all positions of the blade, each ofthe Wall segments being supported from the ,second inner casing member:by a pair of axially spaced circumferentially extend-ing dovetalflanges each including a radially inwardly ex tending wall portion andan inner `end ,portion extending axially away from said rst inner cas-.ing member and lengaging circumferential grooves `in a pair ofcooperating axially spaced circumerentially 4extending anges projectingradially outward from the second inner casing member, the rst innercasing member having a circumieren-tial edge portion projecting axiallytoward said row of segments and defining therewith a .circumferentialclearance space of such width that the segments are prevented frommoving axially `toward .the first inner casing member a sufcientdistance to disengage the cooperating dovetail flanges when the firstfand second `inner teasing members are secured together, the secondinner casing member defining a pressure .chamber between thecircumferentially extending dovetail flanges, and conduit means forsupplying ,iiuid runder pressure to .said pressure chamber whereby thesegments are biased radially outward into .engagement with the adjacentends of the adjustable blades.

BRUCE O. BUCKLAND. GLENN B. iWARREN.

References Cited in the le of this patent UNITED STATES .PATENTS NumberName Date 2,412,365 Sollinger Dec. 10, 1946 '2,488,867 Judson 'Nov.^22,1949 FOREIGN PATENTS Number Country Date A597,46 Germany Oct. 1.4, 1940609,682 Great Britain Oct. 5, 1948

